1. Field of the Technology
The present technology relates to development apparatuses used in image forming apparatuses such as copiers, printers, digital multifunction devices, and the like that form images using a developer, and more specifically relates to development apparatuses that use a two-component developer.
2. Related Art
In a conventional electrophotographic image forming apparatus, after uniformly charging a photosensitive body with a charging apparatus, an electrostatic latent image is formed on this photosensitive body with, for example, a laser beam, and this electrostatic latent image is made visible as a toner image by the development apparatus. After the toner image is transferred to recording paper, the toner image is affixed to the recording paper by a fixing apparatus.
Inside the development apparatus, a developer that includes toner is circulated and conveyed, and toner is appropriately resupplied from a toner cartridge. Included in this resupplied toner is a wax component that melts easily with heat, in order to insure low temperature fixing properties.
In a conventional development apparatus, the conveying speed at which developer is conveyed is slow, and there is a comparatively small amount of wax in the toner, so the toner only slightly condenses and affixes to a conveying member that conveys the developer. Therefore, conventionally nothing has been done to prevent this condensation and affixing.
However, recently, image forming apparatuses have appeared that perform print processing at high speed, and in order to be compatible with these high speed processing devices, wax with a low melting point is used, and there is high tendency for the amount of added wax to be increased. Also, in the case of a high speed processing device, because circulating conveying of developer in the development apparatus is also fast, when wax with a low melting point is used, and the amount of wax blended is increased, there is the problem that toner is more easily condensed due to heat produced during circulating conveying in the development apparatus. Also, when temperature is high, there is the problem that toner affixes to a specific portion of the conveying member. In particular, the vicinity of a toner resupply port is normally in state filled with toner resupplied from the toner cartridge, so frictional heat among developer, and frictional heat between developer and the conveying member, is high, and this is a circumstance in which toner condensation and toner affixing easily occur.
Following is a specific description of toner condensation and toner affixing in a conventional development apparatus, with reference to FIGS. 8 and 9. FIGS. 8 and 9 show a conventional development apparatus, with FIG. 8 being a plan view showing a state in which an upper lid has been provided, and FIG. 9 being a plan view showing a state in which the upper lid is omitted.
As shown in FIG. 8, on the upper face of a case 310 of a development apparatus 300, a toner resupply port 311 is provided in order to resupply toner from a toner cartridge (not shown) in which toner is accumulated.
Also, as shown in FIG. 9, inside the development apparatus 300, a first developer conveying path 301 one end of which faces the toner resupply port 311, and a second developer conveying path 302, are provided in rows, and the developer conveying paths 301 and 302 are partitioned by a partition wall 303. Between both ends of the partition wall 303 and the case 310, respective open portions 304 and 305 are provided, and thus the developer conveying paths 301 and 302 have a structure so as to be in communication with each other via the open portions 304 and 305.
Also, a first screw conveyor 306 is disposed in the first developer conveying path 301, a second screw conveyor 307 is disposed in the second developer conveying path 302, and with rotation of the screw conveyors 306 and 307, developer inside the case 310 is circulated and conveyed between the first developer conveying path 301 and the second developer conveying path 302.
More specifically, toner that has been resupplied from the toner resupply port 311 is conveyed in the first developer conveying path 301 by the first screw conveyor 306 while mixing with magnetic carrier in the rightward direction in FIG. 8, developer in which toner and the magnetic carrier have been mixed is conveyed to the second developer conveying path 302 via the open portion 305 on the right end, then conveyed in the second developer conveying path 302 by the second screw conveyor 307 in the leftward direction in FIG. 8, and again conveyed to the first developer conveying path 301 via the open portion 304 on the left end. The developer is circulated by following this sort of conveying path.
Here, the toner that has been resupplied from the toner resupply port 311 to the first developer conveying path 301 merges with the developer that has been conveyed from the second developer conveying path 302 via the open portion 304 immediately behind the position of that toner resupply port 311, and this merging portion is in a location where accumulation easily occurs. Therefore, particularly in the vicinity of the toner resupply port 311 on the front side of the merging portion, toner easily accumulates, and as a result, toner easily condenses on the first screw conveyor 306.
When toner condensation on the first screw conveyor 306 occurs, pressure concentrates on that portion, and if toner condensation continues, a toner deposit 309 will occur on the first screw conveyor 306. When a toner deposit 309 occurs, the actual conveying performance of the first screw conveyor 306 decreases. Thus, the problem occurs that the toner deposit becomes still larger, resupplied toner spills out from the toner resupply port 311, and rotation of the first screw conveyor 306 stops.
Such a toner affixing problem can be solved by increasing the size of the image forming apparatus itself, or by using a cooling apparatus, but market demands for reduced size of the image forming apparatus are strong, and providing a cooling apparatus results in increased cost, so addressing the toner affixing problem in these ways is difficult.
Consequently, as a means of eliminating such toner affixing, a toner resupply apparatus has been disclosed in which toner condensation is prevented with a coil spring (for example, see JP H6-167880A (referred to below as Patent Document 1)).
In the toner resupply apparatus disclosed in Patent Document 1, as shown in FIG. 8(a) of Patent Document 1, a protrusion (81), which is fixed at one end to a side plate (47) of a toner hopper unit (40Y) and is inserted into a coil spring (82), is provided between an agitator (44) and a toner screw conveyor (42), and is held in a state with a bottom end (821) of the coil spring (82) in contact with a conveying blade (422) of the toner screw conveyor (42). In this state, when the toner screw conveyor (42) starts to rotate, the coil spring (82) is compressed by a rotating action of the conveying blade (422), and when compressed a certain amount, thereafter the coil spring (82) travels over the conveying blade (422) and is restored to an initial shape due to tensile force of the coil spring (82). Because the coil spring (82) bursts when being restored, a toner condensation (73) is broken up ([0032]).
However, in the toner resupply apparatus of above Patent Document 1, the coil spring (82) is required to travel over the conveying blade (422) when being restored, so it is necessary to use a large coil spring in order to reliably allow the spring to be restored. Therefore, there is the problem that the apparatus cannot be made compact. Also, the coil spring (82) is merely inserted into the protruding portion (81) and is in a dangling state, and not fixed, so due to its own weight the coil spring (82) is in contact with the rotating shaft of the toner screw conveyor (42). Accordingly, there is a possibility that the coil spring (82) as a whole will be pushed up along the slope of the face of the conveying blade (422), and in this case, there is the problem that the coil spring (82) is restored to the original state before being adequately compressed, a sufficient bursting effect is not obtained, and it may not be possible to reliably break up the toner condensation.